The relationship between design behaviours and successful design task completion is studied for multidisciplinary design teams. In this research, no observational methods such as audio–visual recordings or ethnographic fieldwork were used, as often the case in design research, but a questionnaire tapping critical behaviours was developed and statistically validated in two separate studies. In addition, this study presents a comprehensive view on the behaviour of design team members. The resulting Design Behaviour Questionnaire for Teams consists of 55 items divided into three main categories (‘design creation’, ‘design planning’, and ’design cooperation’) and 12 scales.